There will be an engine update... Cummins has dropped the Interact System and developed new controls to meet the new emissions standards that went in effect January 1. (FCA is using the current engine under a loophole - engines built prior to January 1 2017 can still be installed until they run out, so FCA likely stockpiled them for the 2017 model year run.) Some spyshots over the last few months hinted at a hood scoop similar to what GM has added on Silverado/Sierra HDs for 2017's new Duramax. There may also be minor tweaks to exterior details and interior features.
The all-new truck is likely still a couple years away. Once the 1500 is fully moved to Sterling Heights, they will gut and rebuild Warren for the new HD as well as the Grand Wagoneer. Since there is an expectation that Warren will build the current 1500 simultaneously with the new one as a fleet model for up to a year, Warren may not shut down for its rebuild until late 2018 or early 2019. That would make the new HD a mid-year 2020 model or an early 2021 model around January 2020. Once Warren is up and running, Saltillo gets shut down for its conversion, although that is expected to be for US/Canada overflow work and Mexico sales.